4.1 Role Analysis in Bluetooth Low Energy Tree Structure

There are three basic roles in the Bluetooth Low Energy tree structure: grandpa node, father node and child node. The purpose of the Bluetooth Low Energy tree structure is that the grandpa node (could be a gateway to cloud) can exchange messages with all other nodes.

In the Bluetooth Core Specification, Bluetooth Low Energy devices can support write, read and notify functions through the Generic Attribute Layer (GATT layer). To implement bi-directional communication between the grandpa node to all its children nodes, use GATT write and GATT notify. For more information, see the BLE5-Stack User's Guide). In this example:

• The grandpa node sends data to its children: GATT write
• Child nodes send data to their ancestors: GATT notify
• The grandpa node receives data from the child nodes: GATT write + GATT notify

To reduce network complexity, the only APIs used are GATT write and GATT notify. When the grandpa node has any data to send to the child nodes, it uses the GATT write command to send the data to the relevant father node. The father node uses the GATT write command to forward the data to one of the child nodes. When child or father nodes need to send data to the grandpa node, they use GATT notify to send the data. If the grandpa node needs to get or poll some information from a father or child node, it also uses the GATT write command to request the node to send the data. The child nodes will use GATT notify to reply to the grandpa node. For more details, see Figure 4.